TIME-RESOLVED W-BAND (95 GHZ) EPR SPECTROSCOPY OF ZN-SUBSTITUTED REACTION CENTERS OF RHODOBACTER-SPHAEROIDES R-26

Transient EPR spectra of protonated and deuterated Zn-substituted reac tion centres of Rhodobacter sphaeroides R-26, measured at a microwave frequency of 95 GHz and an external magnetic field of 3.5 T, are prese nted. The high-field/high-frequency spin-polarized spectrum of the cor related coupled radical pair (P865OA-.)-O-+. after laser flash excitat ion is a very sensitive monitor of the relative orientation of the two g-matrices and the dipolar tenser with respect to each other. Therefo re, detailed structural information of the RC concerning the relative orientation of the primary donor P-856(+.) and the acceptor Q(A)(-.) w ith respect to the axis connecting the two molecules in the RC can be derived. Together with the information obtained by high-field cw-EPR o n single crystals, the enhanced resolution of the polarized high-field spectra allows an unambiguous assignment of the g-matrix of the donor P-865(+.) to the molecular axis system. The experimental results are compared with earlier X-band (9 GHz) and K-band (24 GHz) EPR experimen ts.